Method of refining aluminium-silicon alloys

ABSTRACT

The method consists in that the aluminum-silicon alloy is first treated with flux at a temperature not under 1,500*C, then it is treated with more of the same flux at 900*-1,200*C.

United States Patent [191 Brusakov et al.

[451 Nov. 27, 1973 METHOD OF REFINING ALUMINIUM-SILICON ALLOYS [76]Inventors: Jury Ivanovich Brusakov,

Novo-Izmailovsky prospekt, 37, kv. 42; Irma Solomonovna Livshits, 3linia, 48, kv. 21; Vasily Pavlovich Kiselev, ulitsa Lensoveta, 48, kv.10; Vasily Mikhailovich Cheltsov, prospekt Kosmonavtov, 38, korpus 2,kv. 92, all of Leningrad; Mikhail Pavlovich Avdeev, 7 kvartal, 30, kv.7, Shelekhov, Irkutskoi oblasti; Semen Panteleevich Marin, ulitsa 40 letSovetskoi Ukrainy, 86, kv. 53, Zaporozhie; Miro KhristoforovichAlivoivodich, ulitsa 40 let Sovetskoi, Ukrainy, 46, kv. 21, Zaporozhie;Alexei Kuzmich Kulikov, ulitsa 40 let Sovetskoi Ukrainy, 66, kv. 76,Zaporozhie; Ivan Arkhipovich Berezhnoi, ulitsa Patrioticheskaya, l5, kv.20, Zaporozhie; Pavel Ilich Volpin, prospekt Lenina, 210, kv. 16,Zaporozhie; Leonid Vladimirovich Chernyakhovsky, ulitsaKizhne-Dneprovskaya, 4b, kv. 75, Zaporozhie; Zoya Vasilievna Eltsova,ulitsa 40 let Sovetskoi Ukrainy, 6, kv. 71, Zaporozhie; Lidia NikolaevnaMedvedeva, ulitsa 40 let Sovetskoi Ukrainy, 66, kv. 172, Zaporozhie;Fedor Mifodievich Kolomitsky, ulitsa 21 Partsiezda, l6, kv. 92,Zaporozhie, all of USSR.

[22] Filed:

[21] Appl. No.: 174,533

[30] Foreign Application Priority Data Nov. 11, I970 U.S.S.R 1485657Nov. 11, 1970 U.S.S.R 1485664 [52] US. Cl 75/68 A, 75/93 AC [51] Int. ClC22b 21/06 [58] Field of Search 75/68 A, 93 AC [56] References CitedUNITED STATES PATENTS 2,184,705 12/1939 Willmore 75/68 A 2,255,5499/1941 Kruh 75/68 A 380,577 9/1932 Lightalloy Ltd. 75/68 R FOREIGNPATENTS OR APPLICATIONS 964,792 7/l964 Great Britain 75/68 A OTHERPUBLICATIONS Handbook of Chemistry and Physics; Chemical Rubber Co.;50th Edition; 1969; page B157.

Primary Examiner-L. Dewayne Rutledge Assistant Examiner-M. J. AndrewsAttorney-Holman & Stern [57] ABSTRACT The method consists in that thealuminum-silicon alloy is first treated with flux at a temperature notunder l,500C, then it is treated with more of the same flux at900-1,200C.

3 Claims, No Drawings METHOD OF REFINING ALUMINIUM-SILICO ALLOYS Thepresent invention relates to refining aluminiumsilicon alloys producedin ore-reduction furnaces in order to remove nonmetallic admixtures fromthem.

According to the present invention a flux with a fluosilicic constituentis provided which is useful in refining the diluted aluminium-silicon orother structural aluminium alloys.

Methods are known in the art for refining aluminiumsilicon alloyscontaining more than 30 percent Si by removing non-metallic inclusionsfrom them with the aid of a flux consisting of a mixture of chloridesand fluorides of alkali and/or alkaline-earth metals with preliminarycooling of the alloy down to 900C or down to l,lO-1,300C.

A method is also known in the art for refining casting aluminium-siliconalloys with the aid of a number of general-purpose fluxes consisting ofchlorides and fluorides of alkali and/or alkaline-earth metals.

However, in the known method, when the alloy is preliminarily cooled to900-l,200"C the bulk of the nonmetallic inclusions, functioning asadditional nuclei of crystallization, settles on the walls andbottom ofthe ladle together with silicon (beginning with 1,100C) entraining themetal and thus increasing its losses. At these'temperatures the alloyfeatures a higher viscosity and the process of its refining iscomparatively slow. The known methods are adapted only for fine refiningof the alloy from a small quantity of admixtures.

The fluxes are used in refining the aluminium-silicon alloys not onlyfor removing the nonmetallic admixtures from the alloy, but also forprotecting the alloy surface against oxidation. With this purpose inview the flux melting point should be equal to, or somewhat lower than,the temperature at which the alloy is processed. However, the meltingpoint of the known fluxes used for refining the castingaluminium-silicon alloys is l30-200C higher than the requiredtemperatures which prevents complete protection of the alloy againstoxidation, thus increasing the losses of alloy.

Besides, these fluxes contain a considerable proportion of cryolite orsodium fluoride which raise the cost of the flux.

The main object of the invention resides in selecting the optimumconditions under which the alloy would be best refined from nonmetallicinclusions.

This and other objects are accomplished by the use of a method ofrefining aluminium-silicon alloys produced in ore-reduction electricfurnaces by introducing a flux containing fluorides and chlorides ofalkaline and/or alkaline-earth metals at a temperature of 900-l ,200Cwherein, according to the invention, the alloy is first mixed with aflux at a temperature of not under l,SO0C.

For better protection of the surface of the aluminium-silicon alloyagainst oxidation, it is practicable to use a flux containing thefluosilicate of alkaline metals and having the following composition(per cent):

fluosilicate of alkali metals 38-40 sodium chloride 45-47 potassiumchloridel4-l6 Now the invention will be described in detail by way ofexamples. i

The claimed method of refining aluminium-silicon alloys includes thefollowing operations: as the ladle is being gradually filled with theprimary alloy from the furnace tap hole, said alloy is mixed with 2-4percent of flux (from the total weight of the alloy), said fluxconsisting of a mixture of chlorides and fluorides of alkali and/oralkaline-earth metals.The alloy temperature in the ladle should not belower than 1,500C.The flux introduced at such a temperature is conduciveto coagulation of nonmetallic admixtures, thereby reducing the viscosityof the alloy. The aluminium-silicon alloy preliminarily treated withfluxes is again refined at 900-l,200C, the quantity of the flux being4-6 percent of the total weight of the alloy.

The alloy pretreated by preliminary refining has a lower viscosity sothat refining is sufficiently complete and the losses of the alloy,particularly of silicon, are reduced.

The flux according to the invention wherein the fluoride component isreplaced by fluosilicate improves the protection of the alloy surfaceagainst oxidation at the same time retaining the adequate degree ofrefining the alloy from nonmetallic inclusions.

Besides, said fluosilicate component is markedly cheaper (three timesapproximately) than the fluoride component (cryolite, sodium fluoride,etc.).

It is most practicable to use for these purposes a flux having thefollowing composition (per cent):

fluosilicic component of alkali metals 38-40 sodium chloride 45-47potassium chloride 14-16 The fluosilicic component may be either sodiumfluosilicate or potassium fluosilicate.

Now the invention will be made more apparent by describing the examplesof its realization.

EXAMPLE 1 Let us consider two cases of refining a primaryaluminium-silicon alloy. In both cases the alloy is refined at atemperature of l,200-l,300C. Besides, in the first case the alloy ispreliminarily refined at a temperature of l,600C while in the other casethe alloy is not refined at high temperatures. High-temperature refining(l,600C) produces 670 kg of refined alloy from 1,000 kg of primaryalloy.

When the alloys are refined without hightemperature treatment withfluxes, only 635 kg of refined alloy are obtained from 1,000 kg primaryalloy which means that the alloy losses are increased.

The yield of the alloy owing to additional refining at a temperature ofl,600C increases as much as 5.5 percent.

EXAMPLE 2 Tests at 1,500C have been made of the flux with the followingcomposition:

potassium fluosilicate 38.64 percent sodium chloride 46.21 percentpotassium chloride 15.09 percent The aluminium-silicon alloy was mixedwith the flux of the above-stated composition in the quantity of 2percent of the total weight of the alloy.

A comparison .of the results of refining obtained by the use of theknown and claimed fluxes has shown that the yield of the refined alloyhas remained the same though the quality of the refined alloy withrespect to the nonmetallic inclusions, as determined by a metallographicanalysis has proved to be considerably higher.

Primary Refined alloy alloy Flux composition Yield tons tons K,SiF. NaClKCl 300.0 272.3 90.7 38.64 46.21 15.09 Na;,AlF, NaCl KCl 300.0 270.590.2 20.0 40.0 40.0

duces the prime cost of the alloy.

What is claimed is:

1. A method of refining aluminum-silicon alloys produced inore-reduction electric furnaces comprising introducing into said alloyat a temperature of not under 1,500C a first portion of a fluxcontaining the fluorides and chlorides of alkali and alkaline-earthmetals and adding a second portion of said flux to the alloy at atemperature of 900-l ,200C.

2. A method according to claim 1, wherein said first portion of saidflux is about 2-4 percent by weight of the alloy.

3. A method according to claim 1, wherein the total quantity of saidflux is about 4-6 percent by weight of the alloy.

2. A method according to claim 1, wherein said first portion of saidflux is about 2-4 percent by weight of the alloy.
 3. A method accordingto claim 1, wherein the total quantity of said flux is about 4-6 percentby weight of the alloy.